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296 APPENDIX VII
The question of waste-heat utilization must be considered
upon an economic basis. A further factor to be taken into
account is the question of dividing the heat, which leaves the
laboratory of the furnace, between the regenerators and the waste-
heat steam generator. The higher the temperature at which the
gases are passed to the boiler, the greater its steam-generating
capacity; there is thus a possibility of reducing the cost of the
regenerator. The whole question of the design of the open-hearth
shop and its equipment is a matter of compromise and of balancing
one thing with another in order to secure a desired result—ingot
tonnage of the desired quality, at a profit.
In the foregoing discussion, producer gas has been the only
fuel considered. The fuel question depends largely upon local
conditions for the particular plant. Natural gas and coke-oven
gas eliminate the producer plant; but in many localities natural
gas is becoming scarce and coke-oven gas is not available at a
price and in a quantity which will permit its use. Tar is used in a
few plants, in order to get rid of the enormous quantities produced
by the by-product coking plants. Water gas has been used, as
well as blast-furnace gas mixed with producer or some other gas;
but the use of these last was more or less forced by war conditions.
Pulverized coals are used, as is also oil, which may be atomized by
steam or compressed air, or by mechanical means. Pulverized
coal adds a certain proportion of its ash to the normal cinder,
while finer portions are carried further and about 25 per cent of
ash passes out of the stack suspended in the gases. With most
of these fuels, only the air is preheated.
One of the most important elements in the fuel for an open-
hearth is. sulphur. The less sulphur present the better; it has a
tendency to pass into the cinder and metal, under certain condi-
tions, adding to the expense and time of the melt.